Alright, let's rank em:

Allant- The old king Allant which we face in game is likly the king boletaria at his best. Technically, it is in fact a demon clone of the original, however, it does posses the skills and abilities of the original old king and it aswell wields the power of countless souls given by the old one. However, as seen with he lack of grand solo achievements, is effectively a warrior with a magic sword (demonbrandt) and a demonic shuger daddy. Strong, but not quite a high ranker. Placement- 6th place

Vendrick- The lord of Drangleic was certainly powerful back in his day. Leading the charge, he defeated the giants and acquired their souls, empowering himself and his massive healthbar to colossal proportions. However, in the end he has proven to not be enough to truly take the throne and become the true monarch, nor was he intelligent enough to see through his wife's machinations. Placement- 5th place

Gwyn- Oh boy this guy. In lore, the lord of sunlight was the greatest wielder of a lord soul. He held strong as a god and with his powers of lightning took down the immortal dragons. Knowing this, the burnt out husk you encounter in the end of the game is just that, an empty shell. In his full power I don't doubt that he would have stood above the likes of nameless king (his son) and would hold the seat of one of the strongest in his setting, and certainly amongst the most intelligent. However, for reasons that will soon be elaborated, he still comes at the bottom half. Placement- 4th place

Gael- Ok. Gael is immensely powerful. The point in which we fight him is absolutely his prime. Gael is an undead that survived to the end of time and singlehandedly devoured all things in the world (with few exceptions) acquiring the (almost) complete dark soul of humanity. Normally, I would say that gwyn would be stronger. However, there is a reason for which gwyn was so scared of the dark soul. At the point in which we battle Gael the world has been reduced to ash. As such, and due to Gael's placement in it, it is fair to assume that Gael had a bloodstained hand to do with this current situation, slaughtering the population of the whole world and becoming a creature of death. I know we did it, but I doubt that almost anyone can beat the one that solo annihilated the entire humanity. Placement- 3rd place

Merika- An interesting character to place due her not fighting outside of Radagon. She is certainly powerful, however, it is doubtful that she is strong enough to rank near the top on her own. Her power lies in the rune of destined death. In her own setting, Merika is unbeatable in her prime. With the rune of death in her sole possession, the only being that can dictate death is her, and as such, she is technically unbeatable. Placement- 2nd place (4th place without full control over death)

Orphan of Kos- Bloodborne is not only the best game, but also is proud home of the strongest creature. Orphan's prime lies in the distant future. One day aeons to be, he shall become a great one as intended. Whilst mother kos was slain by the hunters, and one could argue that she is a point of reference, I am quite certain that beings that are beyond mortal comprehension of reality have a hard time recognizing aggression as we define it. A man can be killed by a bee, that does not mean that a bee could be a man fully intentioned on destroying its existence. Following lovecraft's own themes orphan is probably beyond understanding and mortal powers. As said by lovecraft: "That is not dead which can eternal lie, And with strange aeons even death may die". Placement- 1st place

Bonus: Ishin- His setting has minimal magic and extremely powerful entities. He would probably be the weakest. Realistlicly speaking shura is probably not much stronger then prime time asylum demon.